In many instances, it is desirable to effect removal of heavy metal contaminants from liquids. Thus, the presence of metals such as nickel, copper and iron, even in minute quantities, in hydrocarbon charge stocks conducted to catalytic cracking units are known to poison and shorten the life of the cracking catalyst with which such metal contaminated stocks come into contact.
It is also desirable to remove trace metals from lubricating oils or to recover soluble metal catalysts from reactor effluents. The removal of heavy metals such as mercury, silver, cadmium and the like from the water effluents of chemical or photographic plants is also highly desired from an ecological standpoint.
It is known that residues of alkyl lead from combustion of leaded gasoline tend to poison catalysts available for cleaning up automotive exhaust gas by oxidation of carbon monoxide and unburned hydrocarbons in the exhaust. Such poisoning severely shortens the useful life of exhaust combustion catalysts. It has heretofore been proposed that lead-free gasoline be supplied for use in automobiles equipped with emission control devices in the nature of combustion catalysts.
The normal network of petroleum product distribution involves railroad tank cars, pipelines, water borne tankers, tank trucks and bulk storage tanks. For commercial operation these are presently set up to handle different products. For example, the same pipeline will be used to convey a shipment of regular grade gasoline, premium grade gasoline, distillate fuel and other light liquid products in succession.
When leaded gasoline containing tetraethyl lead, tetramethyl lead or a mixture or transalkylation product of the two is contacted with the metal surfaces of transportation and storage facilities a significant amount of lead is left deposited in scale and on the metallic surfaces. Upon using the same facilities for lead-free gasoline, the latter product becomes contaminated to the extent of 0.07 grams of lead per gallon or more. These amounts of lead are sufficient to impair the life of exhaust emission catalysts.
It is accordingly highly desirable to provide selective means for effecting removal of heavy metal contaminant from liquids containing the same without interfering with or otherwise impairing the intended effectiveness of such liquids.